During engine operation, high temperature, high velocity gases flow through the turbine section, passing rows of stationary vanes alternating with rows of rotating blades. Prior turbine vanes have been formed with an airfoil and platforms as a unitary construction, such as by casting. Such unitary constructions can result in lower manufacturing yields. Further, such vanes are typically made of only a single material. However, experience has demonstrated that no single material is ideal for every portion of the vane. In addition, the relatively large size of the past vane constructions made the use of certain materials infeasible.
The vanes must be cooled in order to withstand the high temperature turbine environment. However, in some of the prior vane constructions, manufacturing capabilities and other considerations rendered a number of cooling features and systems infeasible or otherwise not possible. Examples of desired cooling features include cooling channels near the outer surface of the airfoil and thin outer walls. These features can greatly enhance cooling, but have been difficult to achieve in prior vane constructions.